A thermal processing chamber as used herein refers to a device that rapidly heats objects, such as semiconductor wafers. Such devices typically include a substrate holder for holding one or more semiconductor wafers and an energy source for heating the wafers, such as heating lamps and/or an electrical resistance heater. During heat treatment, the semiconductor wafers are heated under controlled conditions according to a preset temperature regime.
Many semiconductor heating processes require a wafer to be heated to high temperatures so that various chemical and physical transformations can take place as the wafer is fabricated into a device. During rapid thermal processing, for instance, semiconductor wafers are typically heated by an array of lights to temperatures from about 300° C. to about 1,200° C., for times that are typically less than a few minutes. During these processes, one main goal is to heat the wafers as uniformly as possible.
During the rapid thermal processing of a semiconductor wafer, it is desirable to monitor and control the wafer temperature. In particular, for all of the high temperature wafer processes of current and foreseeable interest, it is important that the true temperature of the wafer be determined with high accuracy, repeatability and speed. The ability to accurately measure the temperature of a wafer has a direct payoff in the quality and size of the manufactured integrated circuit.
One of the most significant challenges in wafer heating systems is the ability to measure accurately the temperature of substrates during the heating process. In the past, various means and devices for measuring the temperature of substrates in thermal processing chambers have been developed. Such devices include, for instance, pyrometers, thermocouples that directly contact the substrate or that are placed adjacent to the substrate, and the use of laser interference.
In order to use pyrometers in a thermal processing chamber, the pyrometers generally need to be calibrated. Consequently, various calibration procedures currently exist to align the temperature readings of the pyrometers with an absolute and accurate temperature reference. The current state of the art and the most widely used method to calibrate pyrometers in thermal processing chambers is to place in the chambers a semiconductor wafer having a thermocouple embedded in the wafer. The temperature measurements taken from the thermocouple are compared with the temperature readings received from the temperature measuring devices and any discrepancy is calibrated out.
Although this method is well suited to calibrating temperature measuring device, such as pyrometers, it requires a substantial amount of time to calibrate the instruments. As such, a need currently exists for a method of calibrating pyrometers in thermal processing chambers very rapidly without creating a substantial amount of down time. In particular, a need exists for a method of calibrating pyrometers in thermal processing chambers without having to open the chamber, in order to maintain chamber integrity and purity. A need also exists for a simple method for calibrating pyrometers in thermal processing chambers that can be used routinely as a regular check to verify that the optical pyrometry system is properly functioning.